Calorie Deficit on Mounjaro and Wegovy: The Complete Guide

In simple terms: if the energy you take in from food is less than the energy your body burns, your body draws on stored energy — primarily fat — to make up the difference. That gap is the calorie deficit, and it's the same principle whether or not you're on a GLP-1 medicine.

The basic formula

To estimate your deficit, you need two numbers: your daily calorie needs (often called TDEE — total daily energy expenditure) and your daily intake. Subtract intake from needs, and the result is your deficit. A common starting point many people use is a deficit of around 300–500 calories per day for steady, sustainable loss, though the right figure varies by person, body size, and activity. Larger deficits (e.g. a 1,000-per-day target) tend to be harder to sustain and can leave you under-fuelled, especially when GLP-1 medicines are already suppressing appetite.

Why GLP-1 medicines change the picture

Mounjaro (tirzepatide) and Wegovy (semaglutide) act on appetite-regulating pathways, so many people find they naturally eat less without consciously dieting. That can mean a calorie deficit happens almost by default — sometimes a larger one than is comfortable or wise. The risk isn't usually too little deficit; it's slipping into a deficit so deep that protein intake drops, energy crashes, and muscle is lost alongside fat. For more on how the medicine itself influences appetite, see our overview of how Mounjaro works and the 5 mg dose stage.

How to calculate your calorie deficit

A practical approach:

• Estimate maintenance calories using your age, sex, weight, height and activity level. Our calorie estimator walks you through it, and there's a more detailed calorie calculation breakdown if you want the underlying numbers.
• Subtract a moderate deficit — typically 300–500 calories — to get your daily target. Women specifically can find context in our piece on daily calorie needs for women.
• Set a protein floor so the deficit doesn't come out of muscle. Many people on GLP-1s aim for at least ~1.2–1.6 g of protein per kg of body weight, but check what's right for you with your prescriber or dietitian.
• Track for a week or two before adjusting. Weight fluctuates daily; trends over weeks matter more than any single number.

What deficit should you be in?

There is no single "correct" deficit. The NHS Better Health programme broadly suggests around 600 calories below maintenance for many adults aiming to lose weight, but on a GLP-1 the bigger issue is often eating enough — particularly enough protein and fibre — rather than restricting further. You can read the NHS weight-loss plan guidance for general public-health framing. Personalised targets, however, are best set with your prescriber or doctor — they know your full picture.

Common pitfalls when calculating a deficit

• Over-estimating activity. Most people aren't as active as their fitness tracker suggests.
• Under-counting drinks, oils, sauces. These add up quickly and are easy to miss.
• Eating too little on low-appetite days, then over-correcting later. A weekly average matters more than any single day.
• Ignoring protein. A deficit without enough protein risks losing muscle alongside fat — covered more in our meal-planning guide for weight loss.

Foods that make a deficit easier to sustain

On a GLP-1, capacity is limited — so every bite needs to earn its place. Protein-forward meals (chicken, fish, eggs, Greek yogurt, tofu, lean mince), fibre-rich vegetables, and slower-digesting carbs tend to keep you fuller for longer and protect lean mass. Highly processed, calorie-dense foods can blow a day's budget in a couple of bites. Practical structures and food ideas are covered in our diet plan for weight loss and the broader weight-loss diet guide, with sample meal frameworks in our weight-loss diet plans.

The single biggest reason people give up on a calorie deficit isn't motivation — it's friction. Typing every ingredient into a logger after a long day is the fastest way to stop logging at all. GLP Trackr is built to take that friction out, so the deficit you've worked out actually translates into the deficit you live.

Snap, scan, done

The AI food camera lets you point your phone at a plate and get an instant breakdown of calories, protein and macros — no menu hunting, no guessing portion sizes. For packaged foods, the barcode scanner does the same in a second. On low-appetite days when you're barely eating, that speed matters: you can capture a small snack in five seconds rather than skipping the log entirely.

A deficit you can actually see

Set your calorie and protein targets once, and the daily view shows your remaining budget in real time — a built-in calorie deficit tracker rather than a spreadsheet you forget to update. Pair it with weekly weight and measurement logging, and the insights surface what's genuinely moving your results — whether that's protein consistency, step count, or sleep. For a deeper dive into the deficit specifically, see our companion guides on calorie deficit for weight loss and understanding calorie deficits.

Connecting food, dose, and progress in one place

Because GLP Trackr also logs your shot, dose, and side effects, you can see how your appetite and intake naturally shift across the week — useful context if you find your deficit is bigger than you intended on certain days. If anything feels off, that record is something to share with your prescriber. Our guide to calories on a GLP-1 and calorie counter overview explain how the logging side fits the bigger picture.

A note on safety and individual needs

Calorie targets, protein needs, and how aggressively to pursue a deficit are personal decisions — particularly on a prescription medicine. If you're losing weight very quickly, feeling persistently unwell, or experiencing symptoms that worry you (severe abdominal pain, for example — see our note on Mounjaro and pancreatitis), contact your healthcare professional promptly. GLP Trackr is here to help you record and reflect, not to replace your prescriber's advice.

Ready to make your deficit effortless? Point your camera at your plate, watch your protein and calories land in seconds, and see your weekly trend build. GLP Trackr is free to try for 7 days on the App Store and Google Play — give yourself the easiest tracking experience you've ever had.